
ECSS‐E‐ST‐60‐20CRev.1
15November2008
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3.2.8.2 bias
errorontheknowledgeoftheorientationoftheBRFincluding:
• the initial alignment measurement error between the Alignment
ReferenceFrame(ARF)andthe sensorBoresightReferenceFrame(BRF)
(ongroundcalibration)
• theAlignmentStability Error(CalibrationtoFlight)witchisthechange
in the transformation between the sensor
Mechanical Reference Frame
(MRF)andthesensorBoresightReferenceFrame(BRF)betweenthetime
ofcalibrationandthestartofthein‐flightmission
NOTE1 The bias can be for the BRF Z‐axis directional or
therotationalerrorsaroundtheBRFX,Y‐axes.
NOTE2 For definition
of directional and rotational errors
see
B.5.14andB.5.17.
NOTE3 Duetoitsnature,thebiasmetricvalueisthesame
whatevertheobservationareais.
NOTE4 The associated metrics is the MME (see Annex
B.5.7forthemathematicaldefinition).Thedetailed
contributorstothebiasaregivenin
AnnexG.
3.2.8.3 FOV spatial error
error on the measured attitude quaternion due to theindividual spatial errors
onthestars
NOTE1 This error has a spatial periodicity, whose
amplitude is defined by the supplier. It ranges
fromafewpixelsuptothefullcameraFOV.
NOTE2 FOV spatial errors are mainly due to
optical
distortion. These errors can be converted to time
domain using sensor angular rate. Then, from
temporalfrequencypointofview,theyrangefrom
bias to high frequency errors depending on the
motion of stars on the detector. They lead to bias
error in the case of inertial pointing, while
they
contribute to random noise for high angular rate
missions.
NOTE3 The associated metrics is the MDE (see Annex
B.5.11 for the mathematical definition). The
detailed contributors to the FOV spatial error are
givenin
AnnexG.
3.2.8.4 pixel spatial error
Measurement errors of star positions due to detector spatial non uniformities
(including PRNU, DSNU, dark current spikes, FPN) and star centroid
computation(alsocalledinterpolationerror)
NOTE1 Becauseoftheir‘spatial’nature–theseerrorsvary
withthepositionofstarsonthedetector–theyare
well captured by
metrics working in the angular
domain. The pixel spatial errors are then well
defined as the errors on the measured attitude